Sky Spy: Moon, Saturn, Arcturus and Spica illuminate sky

The moon is always impressive, whether viewed with the naked eye or with binoculars or a small telescope. It constantly acts as a pointer to other celestial objects of interest.

Tonight is no exception.

It will be a beautiful sight as it rises above the eastern mountains in the early evening. By 10 p.m., the moon will be in the southeast 16 degrees above the horizon.

Higher above the moon is Spica, the 16th brightest star in the sky. Spica has a distinct blue color which will be overwhelmed by the nearby bright moon.

Spica is actually two stars very close together, both of which have very high temperatures of 22,400 degrees Kelvin and 18,500 degrees Kelvin, respectively, versus a temperature of 5,800 degrees Kelvin for the sun.

Below the moon toward the horizon is Saturn. Tonight the moon is at the center point of the base of an isosceles triangle. The base is formed by Saturn and Spica, and toward the east the apex of the triangle is Arcturus, the fourth brightest star in the sky. Arcturus has a distinct reddish orange color that contrasts nicely with the blue color of Spica.

Arcturus has a surface temperature of 4,290 degrees Kelvin. Stars with a red or orange color have low surface temperatures, and stars with a blue or white color have very high surface temperatures.

Since stars are giant balls of hot gas with thermonuclear reactions in their interiors, they have no true "surface." What we call a star's surface is a hot outer layer that emits light in visible wavelengths enabling us to see the star.

Moon Watch

The full moon was yesterday, and the moon will look nearly full when it rises tonight at 8:27 p.m. The moon will be in waning (growing smaller) gibbous (more than half lit) phase until the last quarter on Tuesday.